The present invention relates to a module containing electric elements such as semiconductor chips or surface acoustic wave devices. In particular, the present invention relates to an electric element built-in module that can be made ultra-thin and is suitable for a high-density packaging. In addition, the present invention relates to a method for manufacturing such an electric element built-in module.
In recent years, with the demand for higher performance and miniaturization of electronic equipment, higher density and higher function for packages in which semiconductor chips are mounted have been desired increasingly. Furthermore, there also is an increasing demand for smaller and higher-density circuit boards on which they are mounted. However, with conventional multilayered circuit boards including glass fiber and an epoxy resin (glass-epoxy multilayered circuit boards) having a penetrating through hole structure formed by drilling, it has become difficult to achieve the high-density packaging. Accordingly, instead of the conventional glass epoxy multilayered circuit boards, circuit boards that allow a connection not by the penetrating through hole but by an inner via hole have been developed actively (for example, JP 6(1994)-268345 A and JP 7(1995)-147464 A).
However, with the current state of the art, even the high-density mounted circuit boards having such an inner via hole structure cannot keep up with the miniaturization of the semiconductor chips. For example, although the pitch of lead electrodes has become as fine as about 50 xcexcm as the wiring of the semiconductor chips becomes finer, the wiring pitch of the circuit boards and the via hole pitch still are about 100 xcexcm. Therefore, the space for leading out the electrodes from the semiconductor chips increases, thus becoming an obstacle to miniaturization of the semiconductor packages.
Also, since the circuit boards are formed with a resin-based material, they have a low thermal conductivity. Thus, as the component packaging achieves a higher density, it becomes more difficult to dissipate heat that is generated from these components. The clock frequency of CPUs is expected to become about 1 GHz in the year 2000, and with the accompanying higher function thereof, the power consumption of the CPUs is expected to reach 100 to 150 W per a chip.
Furthermore, along with the increase in speed and density, it has become difficult to ignore the influence of noise.
Therefore, in circuit boards, not only the improvement of density and function resulting from a finer circuitry but also anti-noise characteristics and heat dissipation characteristics have to be taken into account.
On the other hand, as a form of responding to the miniaturization of the semiconductor chips described above, a chip size package (CSP) has been suggested. In this CSP, a semiconductor chip is flip-chip mounted on a circuit board called an interposer whose back surface has grid electrodes formed two-dimensionally thereon, and electrodes of the semiconductor chip and the grid electrodes are connected via via holes in the circuit board. This makes it possible to lead out the electrodes of the semiconductor chip that have been formed to have a pitch of not more than 100 xcexcm from the grid electrodes having a pitch of about 0.5 to 1.0 mm, allowing an increase in the pitch of the lead electrodes.
As a result, the need for the finer circuit board on which the CSP is mounted has somewhat reduced, and thus inexpensive circuit boards can be used. Moreover, there is an advantage that the CSP can be used as a tested semiconductor package whose reliability is guaranteed. Consequently, compared with a bare chip technique in which a semiconductor bare chip is mounted on a circuit board directly, the cost required for testing chip damages and defective elements and for ensuring the reliability can be reduced while achieving the miniaturization, which is an advantage of the bare chip mounting.
The development of the CSP described above contributes to an advancement of the miniaturization of the semiconductor package.
On the other hand, in information terminals represented by a mobile personal computer and a mobile phone that can deal with information personally thanks to the development of the internet, the demand for smaller and thinner equipment has been intensified. The typical equipment includes a card-size information terminal, in particular. For example, it is expected to be applied more broadly to card-size radio equipment, a mobile phone, a personal identification card and a memory card for music delivery other than to a current credit card. Thus, a thin semiconductor package or active component that can be mounted on the card-size information terminal mentioned above is desired strongly.
When the above-described CSP is used for achieving a thinner semiconductor package, the bump height in the case of flip-chip mounting, or the wire height and the thickness of a sealing resin in the case of wire bonding, will be added to the thickness of the semiconductor chip (about 0.4 mm) and that of the interposer as the circuit board, resulting in the total thickness of about 0.7 mm. Since the total thickness required for the card-size equipment is about 0.3 to 1.0 mm, the semiconductor package has to be still thinner.
The thickness of the semiconductor package can be reduced by TAB (tape automatic bonding) mounting. An opening and a wiring pattern made of a copper foil are formed on a tape-like film of such as polyimide, a semiconductor chip is mounted in the opening, and electrodes protruding toward the opening directly are bonded to electrodes of the semiconductor chip (inner lead bonding). Similarly, electrodes are led out by connecting electrodes protruding from the tape with the circuit board (outer lead bonding). In this manner, the semiconductor package having a thickness substantially equal to the tape thickness (about 100 xcexcm) can be obtained. In some cases, the form of superimposing multiple layers of this TAB mounted product also is suggested.
In any methods, it is needless to say that the semiconductor chip should be as thin as possible, but since the one (a silicon semiconductor, in particular) with a thickness of not more than 100 xcexcm has a poor mechanical strength, such a semiconductor chip sometimes is damaged during the flip-chip mounting, in which a load is applied. Also, when a semiconductor wafer is abraded to be thinner, its mechanical strength decreases, so that the wafer is more likely to break in a later dicing. On the other hand, after being subjected to dicing, it is extremely difficult and economically inefficient to abrade a small semiconductor chip to be thinner.
On the other hand, the thickness of the semiconductor chip can be reduced by prior dicing. In the prior dicing, the semiconductor wafer is diced halfway of its thickness from one surface, and then is abraded from the other surface until reaching the diced portion. This method can provide a semiconductor chip that is cut automatically after abrading. However, even with this method, because each of the semiconductor chips is thin, a load cannot be applied thereto, leading to a difficulty in dealing at the time of mounting.
Also, in the mobile phone or the like, a surface acoustic wave device is used as a component part of a filter for extracting a specific frequency component.
FIG. 7 is a sectional view showing one example of a structure of a conventional surface acoustic wave device built-in module including two surface acoustic wave devices having a filter function. This module is used as, for example, an antenna duplexer used in a radio portion of a mobile phone or the like.
In FIG. 7, numeral 601 denotes surface acoustic wave devices, numeral 602 denotes piezoelectric substrates, numeral 603 denotes comb-shaped electrodes, numeral 604 denotes lead-out electrodes, and numeral 605 denotes metal bumps. Numeral 607 denotes a circuit board, numeral 609 denotes first wiring patterns, numeral 610 denotes second wiring patterns, numeral 611 denotes via holes, numeral 612 denotes a cover, numeral 613 denotes a sealant, numeral 614 denotes internal circuits, and numeral 615 denotes a concave portion.
In the surface acoustic wave device 601, on one surface of the piezoelectric substrate 602 formed of, for example, lithium tantalate, lithium niobate or quartz, the comb-shaped electrode 603 and the lead-out electrodes 604 formed of a metal film containing aluminum as a main component are formed. The metal bumps 605 for an electrical connection with an external circuit are formed on the lead-out electrodes 604.
The circuit board 607 has the first wiring patterns 609 on one surface, the second wiring patterns 610 on the other surface and the internal circuits 614 therein. The first wiring pattern 609, the second wiring pattern 610 and the internal circuit 614 are connected by the via holes 611. A plurality of the surface acoustic wave devices 601 built into the module shown in FIG. 7 and the external circuit are connected via these elements. In order to ensure a space in which the surface acoustic wave devices 601 are mounted, the circuit board 607 has the concave portion 615 in its central portion.
After the surface acoustic wave devices 601 are positioned and placed on the circuit board 607, the first wiring patterns 609 and the metal bumps 605 are electrically connected. When gold bumps are used as the metal bumps 605, heat and ultrasonic wave are used in combination so as to melt the metal bumps 605 for the connection. Alternatively, there also is a case of making the connection using an electrically conductive adhesive. Also, when solder bumps are used as the metal bumps 605, the connection is made by reflowing the solder bumps.
Since the surface acoustic wave device 601 is sensitive to an influence of an external atmosphere, the concave portion 615 of the circuit board 607 finally is sealed airtightly with, for example, the cover 612 formed of a metal plate and the sealant 613 formed of a solder or an adhesive. In this manner, the surface acoustic wave device built-in module used for an antenna duplexer or the like is obtained.
In the above description, as the piezoelectric substrate 602 constituting the surface acoustic wave device 601, a wafer having a thickness of 0.3 to 0.4 mm is used normally. Thus, the conventional surface acoustic wave device built-in module has a thickness of about 1 mm, making it difficult to reduce the thickness of electronic equipment represented by a mobile phone.
Accompanying a rapid advancement of mobile communication equipment in recent years, a still thinner module has been required, leading to an increase in demand for reducing the thickness of the piezoelectric substrate 602. However, since a single crystal material such as lithium tantalate, which is used as the piezoelectric substrate 602, is brittle and easy to break, it is very difficult to use the piezoelectric substrate 602 as thin as, for example, about 0.2 mm in practice during wafer transportation in a photolithography process for forming the comb-shaped electrode on the piezoelectric substrate 602 and when dealing with each of the devices in a process of mounting it on the circuit board 607. Furthermore, in the surface acoustic wave device 601, a commonly used technique is that the surface (the surface on a nonfunctional portion side) opposite to that on which the comb-shaped electrode 603 is formed (the surface on a functional portion side) is roughened so as to prevent a deterioration in characteristics caused by a reflection of an elastic wave from the surface on the nonfunctional portion side. When attempting to reduce the thickness of the piezoelectric substrate 602, the wafer is more likely to break also in this process of roughening the surface on the nonfunctional portion side. Accordingly, with the conventional structure, a thinner component built-in module using the surface acoustic wave device has been difficult to achieve.
It is an object of the present invention to solve the conventional problems described above and to provide a thin and mechanically strong module containing electric elements such as semiconductor chips or surface acoustic wave devices. It also is an object of the present invention to provide a method for manufacturing such an electric element built-in module effectively.
In order to achieve the above-mentioned objects, the present invention has the following structure.
An electric element built-in module according to the present invention includes a wiring pattern, at least two electric elements mounted on the wiring pattern, and a thermosetting resin composition for sealing the electric elements. Upper surfaces of the at least two electric elements and an upper surface of the thermosetting resin composition are substantially flush with each other.
This improves a mechanical strength because the electric elements are sealed with the thermosetting resin composition. Also, such a module can be obtained by grinding or abrading the upper surfaces of the electric elements and the upper surface of the thermosetting resin composition at the same time to achieve a desired thickness. In this case, since the electric elements are sealed with the thermosetting resin composition, the electric elements are not damaged by an external force during the processing. Thus, it is possible to provide a thin electric element built-in module that has a mechanical strength. Also, because at least two electric elements are provided, a high density module mounting can be achieved. Furthermore, by dividing the module by each of the electric elements, it is possible to provide a thin electric element built-in package that has mechanical strength.
In the electric element built-in module described above, it is preferable that at least one (more preferably, all) of the electric elements includes a functional portion and a connection electrode on a surface on a side of the wiring pattern, and the connection electrode is connected to the wiring pattern. This makes it possible to grind or abrade the surface opposite to the side of the wiring pattern of the electric element (the surface on a nonfunctional portion side). Thus, a thin module having a desired thickness can be provided.
Also, in the electric element built-in module described above, at least one of the electric elements may be at least one element selected from the group consisting of a semiconductor chip, a chip resistor, a chip capacitor and a chip inductor.
Alternatively, in the electric element built-in module described above, at least one of the electric elements may be a surface acoustic wave device.
When using the surface acoustic wave device as the electric element, it is preferable that a surface of the surface acoustic wave device on the side of the wiring pattern is provided with a functional portion and a space holding structure for preventing excitation and propagation of a surface elastic wave from being obstructed in the functional portion. The surface of the surface acoustic wave device on the functional portion side faces the wiring pattern, and therefore, the surface on the nonfunctional portion side can be ground or abraded. Thus, it is possible to provide a thin module having a desired thickness. Also, by providing the space holding structure, it is possible to fill a resin between the functional portion and the wiring pattern, thus improving the mechanical strength. Consequently, it is possible to prevent damages owing to an external force during processing for reducing the thickness.
It is preferable that the space holding structure is formed of a film-like resin composition. This improves an adhesion to a sealing resin, thereby obtaining a highly reliable module.
Also, in the electric element built-in module described above, it is preferable that the upper surfaces of the at least two electric elements both have a surface roughness Rz of 0.5 to 50 xcexcm. Furthermore, it is preferable that the upper surfaces of the at least two electric elements and the upper surface of the thermosetting resin composition that are substantially flush with each other both have a surface roughness Rz of 0.5 to 50 xcexcm. In this case, the surface roughness Rz denotes a mean roughness of ten points. The surface roughness Rz of smaller than 0.5 xcexcm causes breakage of a connected portion of the electric elements and the wiring pattern owing to the above-described processing of the upper surfaces and cracking at an interface between the electric elements and the resin composition. On the other hand, the surface roughness Rz of larger than 50 xcexcm brings about breakage and cracking of the electric elements. Furthermore, when using the surface acoustic wave device as the electric element, the surface roughness Rz that is out of the above range deteriorates frequency characteristics.
Moreover, in the electric element built-in module described above, it is preferable that the thermosetting resin composition contains an inorganic filler and a thermosetting resin. By selecting the inorganic filler and the thermosetting resin, it is possible to achieve a module having a desired performance.
It is preferable that the thermosetting resin contains an epoxy resin, a phenolic resin or a cyanate resin as a main component. This is because these resins have excellent heat resistance and insulation reliability.
Also, it is preferable that the inorganic filler is at least one inorganic filler selected from the group consisting of Al2O3, MgO, BN, AlN and SiO2. This is because various performances of the module can be secured. By changing materials for the inorganic filler, it becomes possible to control a coefficient of thermal expansion, a thermal conductivity and a dielectric constant of the thermosetting resin composition. When using Al2O3, it is possible to achieve a module that has a reduced coefficient of thermal expansion and an excellent thermal conductivity. When using SiO2, the dielectric constant can be controlled, and the coefficient of thermal expansion also can be reduced. By selecting the other materials of AlN, MgO or BN, it is possible to achieve a module having a still better thermal conductivity.
For example, by bringing the coefficient of thermal expansion of the resin composition substantially equal to that of the electric element, the cracking and the deterioration in connection reliability due to a temperature change can be prevented. Also, by raising the thermal conductivity of the resin composition, heat dissipation characteristics can be improved when an electronic component is a semiconductor chip requiring heat dissipation. Moreover, by lowering the dielectric constant of the resin composition, it is possible to reduce a high-frequency loss. In the module of the present invention, another electric element can be mounted on the wiring pattern on the side opposite to the sealed electric elements. In this case, the inorganic filler contained in the thermosetting resin composition also can be selected according to characteristics required for this another electric element.
Also, in the electric element built-in module described above, the wiring pattern may be formed on a surface of a circuit board. This makes it possible to obtain a circuit board efficiently on which thin electric elements are mounted.
Alternatively, the wiring pattern may be formed on a surface of a support. By peeling off the support, it is possible to obtain an electric element built-in package that can be mounted on a wiring board or the like. Alternatively, on the exposed wiring pattern, other electric elements can be mounted.
In this case, it is preferable that the support is formed of an organic film or a metal foil.
Furthermore, in the electric element built-in module described above, it is preferable that at least one of the electric elements is connected to the wiring pattern via a bump. This can achieve a highly reliable electrical connection in an efficient manner.
Next, a method for manufacturing an electric element built-in module of the present invention includes mounting at least one electric element, one of whose surface is provided with a functional portion and a connection electrode, on a wiring pattern so that the one surface faces the wiring pattern, sealing the electric element with a thermosetting resin composition from a side of the other surface of the electric element, and grinding or abrading the electric element sealed with the thermosetting resin composition from the side of the other surface of the electric element.
According to the above method, a thick electric element is mounted, sealed with the thermosetting resin composition, and then ground or abraded from the surface on the nonfunctional portion side. Since the electric element is reinforced by the resin composition, it is possible to alleviate a mechanical impact and load applied to the electric element during grinding or abrading. Thus, a thin electric element built-in module can be obtained without breaking the electric element. In addition, since the electric element is sealed with the resin composition during grinding or abrading, it is possible to prevent contamination of the electric element and an electrically connected portion.
In the above-described method for manufacturing the electric element built-in module, it is preferable that a bump is formed on the connection electrode of the electric element, and the electric element is mounted on the wiring pattern using the bump and an electrically conductive adhesive. This makes it possible to perform processing at a temperature lower than that in the case of a solder connection.
Alternatively, in the above-described method for manufacturing the electric element built-in module, a bump is formed on the connection electrode of the electric element, and the electric element may be mounted on the wiring pattern using the bump and a sheet in which an electrically conductive filler is dispersed. This eliminates the need for a process of filling a sealing resin between the electric element and the wiring pattern. In addition, it also is possible to address a fine connection pitch.
Alternatively, in the above-described method for manufacturing the electric element built-in module, a bump is formed on the connection electrode of the electric element, and the electric element may be mounted on the wiring pattern by connecting the bump and the wiring pattern in an ultrasonic manner. This makes it possible to reduce a thermal load on the electric element.
Also, in the above-described method for manufacturing the electric element built-in module, it is preferable further to include filling and curing a resin between the electric element and the wiring pattern, after mounting the electric element on the wiring pattern and before sealing the electric element with the thermosetting resin composition. This makes it possible to protect a connected portion of the electric element and the wiring pattern with the sealing resin (what is called an underfill). Also, the electric element and the connected portion can be prevented from being damaged by a pressure applied in a subsequent process of sealing with the thermosetting resin composition.
Moreover, in the above-described method for manufacturing the electric element built-in module, the electric element can be sealed with the thermosetting resin composition by overlaying an uncured sheet-like object formed of the thermosetting resin composition onto the other surface of the electric element, followed by heating and compression. This makes it possible to seal the electric element with the thermosetting resin composition by a simple process.
Alternatively, in the above-described method for manufacturing the electric element built-in module, the electric element also can be sealed with the thermosetting resin composition by applying an uncured paste-like object formed of the thermosetting resin composition from the other surface of the electric element under a vacuum or a reduced pressure, followed by heating. By applying the paste-like object under a vacuum or a reduced pressure, the paste-like object can be filled thoroughly.
It is preferable that the heating after applying the paste-like object is carried out at an atmospheric pressure or larger. This can reduce voids in the thermosetting resin composition.
In the above method, when the electric element is sealed by overlaying the uncured sheet-like object onto the other surface of the electric element, followed by heating and compression, it is preferable that a temperature of the heating is equal to or lower than a cure starting temperature of the thermosetting resin contained in the resin composition. This can reduce a pressure during the compression. Also, since the thermosetting resin is in the uncured state, the subsequent grinding or abrading becomes easier.
Similarly, when the electric element is sealed by applying the uncured paste-like object from the other surface of the electric element, followed by heating, it is preferable that a temperature of the heating is equal to or lower than a cure starting temperature of the thermosetting resin contained in the resin composition. This can reduce voids remaining in the resin composition. Also, since the thermosetting resin is in the uncured state, the subsequent grinding or abrading becomes easier.
Also, in the above-described method for manufacturing the electric element built-in module, it is preferable that the thermosetting resin composition contains at least 70 wt % to 95 wt % of an inorganic filler and 5 wt % to 30 wt % of a thermosetting resin. By selecting suitably a type of the inorganic filler that is contained with a high concentration, a module having a desired performance can be obtained. For example, by bringing the coefficient of thermal expansion of the resin composition substantially equal to that of the electric element, it is possible to obtain a module that is highly resistant to temperature changes. Also, by improving the heat dissipation characteristics of the resin composition, it is possible to obtain a module that is suitable for an electric element generating a large amount of heat. Moreover, by using an inorganic filler with a low dielectric constant, it is possible to obtain a module having excellent high-frequency characteristics.
Furthermore, the above-described method for manufacturing the electric element built-in module further may include making a division into a desired shape, after grinding or abrading the electric element sealed with the thermosetting resin composition. The thickness is reduced while maintaining a large size, and then the division is made, thus making it possible to produce a thin low-cost electric element package in an efficient manner.
Moreover, in the above-described method for manufacturing the electric element built-in module, the wiring pattern may be formed on a surface of a circuit board. This makes it possible to obtain a circuit board efficiently on which thin electric elements are mounted.
Alternatively, in the above-described method for manufacturing the electric element built-in module, the wiring pattern may be formed on a surface of a support. In this case, an organic film or a metal foil can be used as the support.
In this case, the above-described method further may include peeling off the support, after grinding or abrading the electric element sealed with the thermosetting resin composition. By peeling off the support, it is possible to obtain an electric element built-in package that can be mounted on the circuit board. Alternatively, other electric elements can be mounted on the wiring pattern that is exposed by the peeling off. Since the support is peeled off after the grinding or abrading, the electric element and the wiring pattern can be prevented from being contaminated during the grinding or abrading.
The above-described method further may include, after peeling off the support, forming a wiring pattern by laminating a prepreg for a circuit board provided with a through hole in a thickness direction filled with an electrically conductive paste and a metal foil in this order on a surface on a side of the wiring pattern exposed by the peeling, followed by heating and compression, and then etching the metal foil. This makes it possible to obtain a module having a multilayered structure provided with an inner via hole.
Alternatively, the above-described method further may include, after sealing the electric element with the thermosetting resin composition and before grinding or abrading the electric element sealed with the thermosetting resin composition, peeling off the support, and forming a wiring pattern by laminating a prepreg for a circuit board provided with a through hole in a thickness direction filled with an electrically conductive paste and a metal foil in this order on a surface on a side of the wiring pattern exposed by the peeling, followed by heating and compression, and then etching the metal foil. This makes it possible to obtain a module having a multilayered structure provided with an inner via hole.
The above-described method further may include, after forming the wiring pattern by etching the metal foil, forming at least one second wiring pattern by laminating a prepreg for a circuit board provided with a through hole in a thickness direction filled with an electrically conductive paste and a second metal foil in this order on a surface on a side of the wiring pattern obtained by the etching, followed by heating and compression, and then etching the second metal foil. This makes it possible to obtain a module having a further multilayered structure provided with an inner via hole.
Also, in the above-described method for manufacturing the electric element built-in module, it is preferable that the electric element and the thermosetting resin composition are ground or abraded at the same time so as to be substantially flush with each other. By grinding or abrading them at the same time, a thin module can be obtained easily. In addition, the electric element and the connected portion of the electric element and the wiring pattern can be prevented from being damaged during the grinding or abrading.
Moreover, in the above-described method for manufacturing the electric element built-in module, it is preferable that the grinding or abrading is carried out by an abrading method using an abrasive. In this manner, it is possible to apply a lapping process, which generally is used in a manufacturing process of semiconductor chips, to the manufacturing method of the present invention, and therefore existing facilities can be utilized.